Thermal sensor system and method based on current ratio

ABSTRACT

A thermal sensor system which includes a thermal sensor and a voltage control network which applies a reference voltage level and a delta voltage level to the same or different thermal sensors. The thermal sensor develops a reference current signal in response to the reference voltage level and a delta current signal in response to the delta voltage level. A current gain network adjusts gain of the delta current signal. A current compare sensor, which is responsive to the reference current signal and the delta current signal, provides a comparison metric. A controller controls the current gain network to adjust gain of the delta current signal while monitoring the comparison metric to determine a gain differential value indicative of a current ratio between the current signals. The controller determines a temperature value based on the gain differential value. A LUT may be used to retrieve the temperature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the co-pending U.S. patent applicationentitled THERMAL SENSOR SYSTEM AND METHOD BASED ON CURRENT RATIO, SerialNumber (NS30087HC) which is concurrently filed herewith, which has acommon assignee and at least one common inventor, and which isincorporated by reference herein for all intents and purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to thermal sensors, and moreparticularly to a thermal sensor system that determines a current ratiothrough one or more thermal sensors for measuring temperature.

2. Description of the Related Art

Conventional thermal (or temperature) sensors may rely upon the thermalcoefficient of resistance requiring per-part calibration. Some sensorssense the analog voltage difference between 2 sensors at a fixed currentas a metric for temperature variability. Most sensors rely on PTAT(proportional to absolute temperature) voltage relationships, whereasothers rely on PTAT and CTAT (complementary to absolute temperature)comparisons. Accurate thermal monitoring usually requires either largearea circuitry and/or the use of fabrication-enabled calibration ofanalog components (i.e. trimming or fuse controls). These solutions tendto be costly, either in terms of needing significant die area orrequiring significant additional support (e.g., test, PE, bringup,etc.). It is also desired to accurately measure temperature within alarge temperature range.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and is notlimited by the accompanying figures, in which like references indicatesimilar elements. Elements in the figures are illustrated for simplicityand clarity and have not necessarily been drawn to scale.

FIG. 1 is a simplified block diagram of an electronic system including atemperature measurement select and control block and one or more thermalsensor blocks implemented according to one embodiment;

FIG. 2 is a block diagram of the temperature measurement select andcontrol block of FIG. 1 implemented according to one embodiment forinterfacing one or more of the thermal sensors shown implemented as “M”diodes, individually labeled D1, . . . , DM;

FIG. 3 is a schematic and block diagram of a temperature measurementselect and control system according to one embodiment using a comparatorwhich may be used as the temperature measurement select and controlblock of FIG. 1 coupled to N thermal sensing diodes;

FIG. 4 is a schematic and block diagram of a temperature measurementselect and control system according to a voltage controlled oscillator(VCO) embodiment which may be used as the temperature measurement selectand control block of FIG. 1;

FIG. 5 is a schematic and block diagram of a temperature measurementselect and control system according to another embodiment using a pairof VCOs which may be used as the temperature measurement select andcontrol block of FIG. 1;

FIG. 6 is a schematic and block diagram of a temperature measurementsystem implemented according to an alternative embodiment in which aportion of the temperature measurement select and control block of FIG.1 is instead distributed with each of the thermal sensors which areselectively coupled to a central temperature control block;

FIG. 7 is a schematic and block diagram of a temperature measurementselect and control system according to another embodiment withprogrammable parameters to expand the overall temperature range whichmay be used as the temperature measurement select and control block ofFIG. 1;

FIG. 8 is a schematic diagram of an exemplary embodiment of theprogrammable current mirror blocks of FIG. 7 implemented according toone embodiment;

FIG. 9 is a diagram of a temperature range mode select table that may bestored within the memory of FIG. 7 and which includes the values tofacilitate mode selection for each of multiple predetermined temperaturesubranges;

FIG. 10 is a diagram of a temperature versus gain lookup table which maybe stored within the memory of FIG. 7 and which lists an IDAC gaindifferential value for selected temperature values within eachtemperature subrange of the overall temperature range;

FIG. 11 is a simplified block diagram of the oscillation detector ofFIG. 7 according to one embodiment;

FIG. 12 is a flowchart diagram of a calibration procedure according toone embodiment which may be performed by the system of FIG. 7 fordetermining and storing gain values corresponding to temperature values;and

FIG. 13 is a flowchart diagram of a temperature measurement procedureaccording to one embodiment which may be performed by the system of FIG.7 for measuring temperature.

DETAILED DESCRIPTION

The following description is presented to enable one of ordinary skillin the art to make and use the present invention as provided within thecontext of a particular application and its requirements. Variousmodifications to the preferred embodiment will, however, be apparent toone skilled in the art, and the general principles defined herein may beapplied to other embodiments. Therefore, the present invention is notintended to be limited to the particular embodiments shown and describedherein, but is to be accorded the widest scope consistent with theprinciples and novel features herein disclosed.

A thermal sensor system disclosed herein provides a compact,digital-friendly, thermal measurement system that does not requireexplicit calibration or fuses and that is relatively insensitive toprocess and source voltage. It accomplishes this by using a networkdeveloping currents derived through one or more thermal sensors. Theindicator of temperature, however, is not the actual measured current atone operating voltage applied to the thermal sensor, but the ratio ofcurrents for two different applied voltages. The voltages may be appliedsequentially at two different times to the same sensor or simultaneouslyto two different sensors. In one embodiment, the ratio of current may bedetermined by adjusting a gain value and using a comparator or the liketo sense relative current values. In another embodiment, the ratio ofcurrent may be determined by adjusting gain and using a voltagecontrolled oscillator (VCO) or the like to sense the relative current.In general, temperature is derived based on a ratio of current levelsand/or periods that result with application of at least two differentvoltage levels applied to at least one thermal sensor. The ratio factorstend to cancel out process and other implementation specific parameters.

In various embodiments, one or more diodes are used as the thermalsensor(s). The current level of a forward-biased diode variesexponentially so that the overall current change through a diode of agiven size may be limited to a corresponding current range. In a fixedconfiguration, the limited current range limits measurement to within acorresponding temperature range. Special techniques could be used toextend the temperature range while achieving accuracy, such asmechanisms enabling post-fabrication tuning or the like. Also, since thecurrent of a forward-biased diode changes by order of magnitude and thetemperature is otherwise not known in advance, circuit reliabilityissues should be resolved to prevent over-current conditions which mayfurther cause malfunction or even catastrophic failure of one or moredevices or components.

At least one embodiment operates with multiple configuration modes toincrease the temperature range while providing accuracy and reliabilitymanagement. Each configuration mode has a different device size, adifferent “effective” device size, and different diode voltages whichare collectively optimized for a different temperature subrange withinan extended temperature range. Logic control manages the transitionbetween the modes based on sensing parameters indicative of thetemperature. At least two different sized thermal sensors may be used toadjust device size. The effective device size may further be adjusted byadjusting bias gain. Further, the reference and delta voltages may bothbe adjusted for each particular temperature subrange. For example, thethermal sensor voltages may be increased at the lower temperaturesubranges to increase corresponding thermal sensor currents, anddecreased the higher temperature subranges to decrease correspondingthermal sensor currents to maintain current limits within optimaloperating levels. Any one or more of these methods may be used alone orin combination to increase the overall temperature range by anypracticable amount.

FIG. 1 is a simplified block diagram of an electronic system 100including a temperature measurement select and control block 102 and oneor more thermal sensor blocks 104 implemented according to oneembodiment. As shown, N thermal sensors 104, individually numberedthermal sensor 1, thermal sensor 2, . . . , thermal sensor N, aredistributed in the system in which N is any positive integer greaterthan zero. Each thermal sensor 104 is located at a corresponding “site”for determining the temperature at that location, and develops acorresponding sense signal S1-SN provided to the temperature measurementselect and control block 102. The temperature measurement select andcontrol block 102 accesses and activates a selected one or more of thethermal sensors 104 for determining temperature at the corresponding oneor more sites.

The electronic system 100 may be implemented on an integrated circuit(IC) or chip such as, for example, within a system-on-chip (SOC) or aspart of an embedded processing system or the like. In this case,multiple thermal sensors 104 may be provided to determine thetemperature at corresponding locations of the chip. Alternatively, theelectronic system 100 may be implemented in a discrete manner in whichthe temperature measurement select and control block 102 and the one ormore thermal sensors 104 may each be implemented on a separateintegrated circuit (IC) or otherwise may include any combination of oneor more ICs or semiconductor chips or the like. The electronic system100 may be configured for any type of application, such as communicationsystems, computer systems, sensing devices, etc., and for any one ormore of consumer, industrial, commercial, computing, and/or automotivefields.

Although multiple thermal sensors 104 are shown, N may also be one for aconfiguration with only one thermal sensor 104. The thermal sensors 104are each depicted herein as a diode (PN junction), although it isunderstood that alternative sensor types or configurations are possible,such as a diode-coupled PNP bipolar junction transistor (BJT) or an NPNtransistor or the like.

FIG. 2 is a block diagram of the temperature measurement select andcontrol block 102 implemented according to one embodiment forinterfacing one or more of the thermal sensors 104 shown implemented as“M” diodes, individually labeled D1, . . . , DM. The thermal sensingdiodes described herein are shown referenced to a ground or COM (cathodecoupling), where it is understood that alternative configurations arecontemplated, such as referencing the anodes to an upper source voltagesuch as VDD or the like. The circuitry applying voltage may be modifiedaccordingly to achieve the same or similar results. The number M is alsoa positive integer greater than zero and may be the same or differentfrom N. In one embodiment, for example, each thermal sensor 104incorporates multiple individual thermal sensing devices in which M is amultiple of N. Alternatively, M=N in which each thermal sensor 104includes one thermal sensing device. A voltage control block 202 appliesone or more different reference and offset voltages to a correspondingone or more of the diode(s) D1-DM to develop corresponding reference andoffset currents I₁-I_(M) sensed by a current gain control block 204.

The current gain control block 204 applies corresponding gains (e.g., X,. . . , Y) to each of the currents I₁-I_(M) to develop correspondingcurrents XI₁-YI_(M) to a current compare sensor 206. In one embodiment,X=Y in which the same gain value is applied to each current. In anotherembodiment, a different gain value may be applied to each current inwhich X, . . . , Y denote corresponding and possibly different gainvalues. The current compare sensor 206 compares amplified current valuesand develops at least one comparison metric CM to a controller 208.

The controller 208 controls the voltage control block 202 and thecurrent amplification control block 204 while monitoring the comparisonmetric CM for making a thermal measurement at a selected site. In oneembodiment, the controller 208 applies a site select value SSEL toselect a diode at a selected site or location. The controller 208asserts a voltage select value VSEL for selecting voltage applied to theselected diode. In one embodiment, the controller 208 asserts a gainvalue G to the current gain control block 204 for adjusting gain of anoffset current relative to a reference current to provide acorresponding gain differential value which is indicative of a ratio ofthe reference and offset currents. The “values” described herein may bedigital values, although analog value or signals are also contemplated.In one embodiment, the comparison metric CM is an output of a comparatorwhich indicates a threshold condition. In an alternative embodiment, thecomparison metric CM is a frequency signal output of a controlledoscillator, such as a VCO or current-controlled oscillator (ICO) or thelike. The controller 208 monitors the comparison metric while adjustinggain to determine a gain differential value. The gain differential valuemay then be used to determine the temperature provided as an outputvalue T.

The temperature measurement select and control block 102 is shown ingeneralized form and applies to any one or more of multiple embodimentsor configurations. In one embodiment, for example, only one diode D1 maybe provided in which the voltage control block 202 sequentially appliestwo different reference and offset voltage levels to the same diode, andthe current compare sensor 206 compares corresponding amplified currentvalues for providing CM. In an alternative embodiment, a pair of diodes(e.g., D1 and D2) may be provided at each site in which the voltagecontrol block 202 simultaneously applies the reference and offsetvoltage levels to the two different co-located diodes, and the currentcompare sensor 206 compares the corresponding amplified current valuesfor providing CM.

In one embodiment, for example, each thermal sensor 104 at each of thesites may include a single sensor, such as a single one of the diodesD1-DM, in which case the controller 208 controls the voltage controlblock 202 to sequentially apply a reference voltage level and an offsetvoltage level to the single diode for making a temperature measurement.In another embodiment, each thermal sensor 104 at each of the sites mayinclude at least a pair of equivalent (or matched) diodes, in which thecontroller 208 controls the voltage control block 202 to apply thereference and offset voltage levels to the pair of diodes for making ameasurement at that location. In yet another embodiment, each thermalsensor 104 at each of the sites may include at least a pair of diodeswith significantly different sizes. As further described herein, sincethe current level of a forward-biased diode varies exponentially, anygiven diode may allow measurement only within a corresponding limitedtemperature range without exceeding maximum current limits. A differentsized diode, along with different gain values and different diodevoltage levels enables a different current range and thus a differenttemperature subrange. Thus, diodes of different sizes may be used toextend the overall temperature range for a given configuration.

FIG. 3 is a schematic and block diagram of a temperature measurementselect and control system 300 according to one embodiment using acomparator which may be used as the temperature measurement select andcontrol block 102 coupled to N thermal sensing diodes. A voltage selectblock 302 provides a first diode voltage VD1 to the positive input of afirst amplifier 304, which has its negative input coupled to a node 306.Node 306 is coupled to the anode of a reference diode DR and to thesource of an N-type field-effect transistor (FET) N1. The cathode of DRis coupled to a common node COM, which is any common positive, negativeor ground reference voltage. An unlabeled triangular ground symbol isused throughout the Figures to denote COM unless otherwise specified.The output of the amplifier 304 asserts a bias voltage VB1 to the gateof N1, which has its drain coupled to the drain and gate of a P-type FETP1 at a node 309. The source of P1 is coupled to a source voltage, suchas VDD or the like. VDD is a source voltage relative to COM and isrepresented in the Figures by a pull up horizontal line (e.g., labeled“VDD” coupled to the source of P1). An unlabeled pull up horizontal linesymbol is intended to reference VDD unless otherwise specified.

Node 309 is further coupled to a compensation current digital to analogconverter (IDAC) 308, which includes a first array 310 of P P-type FETsand a second array 312 of P P-type FETs. Each P-type FET of the array310 has its drain coupled to a node 314 and its gate coupled to node309. Each P-type FET of the array 312 has its drain coupled to a sourceof a corresponding P-type FET of the array 310 and its source coupled tothe source voltage VDD. The gate of each P-type FET of the array 312 iscoupled to a corresponding bit of an offset compensation register 316storing a digital offset compensation value O with P bits O₁, O₂, . . .O_(P). Node 314 is coupled to the positive input of a comparator 318,having a negative input receiving a divided source voltage (e.g., VDD/2)and its output providing a compare metric CX.

The voltage select block 302 provides a second diode voltage VD2 to thepositive input of a second amplifier 320, which has its negative inputcoupled to a node 322. Node 322 is coupled to the output of an analogmultiplexer (MUX) 324 and to the source of an N-type FET N2. Each inputof the MUX 324 is coupled to the anode of a corresponding one of Ndiodes D1, D2, . . . , DN, each corresponding to one of the N thermalsensors 104. The cathode of each of the diodes D1-DN is coupled to COM.In an alternative embodiment in which there is only a single thermalsensor 104, the MUX 324 may be omitted and the diode is coupled directlyto N2.

The output of the amplifier 320 asserts a bias voltage VB2 to the gateof N2, which has its drain coupled to the drain and gate of a P-type FETP2. The source of P2 is coupled to the source voltage VDD, and its gateis further coupled to a node 321 which is coupled to a primary IDAC 325.The IDAC 325 includes a first array 326 of Q P-type FETs and a secondarray 328 of Q P-type FETs. Each P-type FET of the array 326 has itsdrain coupled to a node 330 and its gate coupled to node 321. EachP-type FET of the array 328 has its drain coupled to a source of acorresponding P-type FET of the array 326 and its source coupled to thesource voltage VDD. The gate of each P-type FET of the array 328 iscoupled to a corresponding bit of a DAC gain register 332 storing a gainvalue G with Q bits G₁, G₂, . . . G_(Q). Node 330 is coupled to thedrain and gate of another N-type FET N3 which has its source coupled toCOM. The gate of N3 is coupled to the gate of another N-type FET N4having its source coupled to COM and its drain coupled to node 314.

The CX output of the comparator 318 is provided as the comparison metricto the input of a controller 334, which has a first output providing avalue VSEL to the voltage select block 302 for controlling assertion ofthe diode voltages VD1 and VD2, a second output providing a location or“site” select value SSEL to a control input of the MUX 324 for selectingone of the diodes D1-DN located at corresponding locations, a thirdoutput providing the offset compensation value O, a fourth outputproviding the gain value G, and a fifth output providing a determinedtemperature value T indicative of temperature. In one embodiment, eachof the values VSEL, SSEL, G, O and T are multiple bit digital controlvalues.

The voltage select block 302 may include one or more programmablevoltage sources or one or more static voltage reference blocks forproviding the diode voltages VD1 and VD2. In one embodiment, eachprogrammable voltage source or static voltage reference block isimplemented with at least one bandgap voltage reference source(programmable or static) providing a source or reference voltage whichis independent of temperature to improve temperature measurementaccuracy.

In one embodiment, the compensation IDAC 308 is generally matched withthe primary IDAC 325. Thus, for example, each P-type FET of the arrays310 and 312 is generally matched with a corresponding P-type FET in thearrays 326 and 328. In one embodiment, the IDACs 308 and 325 are bothimplemented in a linear fashion in which the current mirror legs arematched with each other so that each bit contributes about the sameamount of current. In another embodiment, the IDACs 308 and 325 are bothimplemented in a binary weighted manner in which each successive currentleg contributes a multiple level of current. Alternative current mirrorgain configurations are contemplated and combinations of these and othermethods are contemplated.

The temperature measurement select and control system 300 applies afirst reference voltage to the reference diode DR and applies a second“delta” voltage to a selected site diode to develop a reference currentin one current branch and a “delta” current in a second current branch.The temperature measurement select and control system 300 determines again differential value by applying gain to the delta current until thecurrents in the different branches substantially match each other. Thegain differential value is thus indicative of the current ratio whichmay be used to determine the temperature value T indicative oftemperature.

The voltage VD1 (used as the reference voltage) is applied to thereference diode DR via voltage-follower amplifier 304 to induce a firstcurrent ID1 (reference current) through DR, and the voltage VD2 (used asthe delta voltage) is applied to a selected one of the diodes D1-DN viavoltage-follower amplifier 320 to induce a second current ID2 (deltacurrent) through the selected thermal sensor diode. P1, the offsetcompensation network 308, and N4 collectively operate to mirror andamplify ID1 into the node 314. Similarly, P2, the IDAC 325, N3 and N4collectively operate to mirror and amplify ID2 into the node 314. Thecomparator 318 asserts CX responsive to a difference between theamplified and mirrored currents. As further described below, thecontroller 334 performs at least one procedure to match the currentbetween the current mirror branches by adjusting relative gain betweenthe branches, and then to determine the temperature value T based on themeasured gain differential value.

The current ID through a diode D is determined according to thefollowing equation (1):

ID=I _(S) ·AD·e ^(VD/VT)  (1)

where I_(S) is the reverse bias saturation current (or scale current),AD is the area of the diode, VD is the diode voltage applied across thediode, and VT is the thermal voltage. The thermal voltage VT isdetermined as VT=k·T/q·∝ in which k is the Boltzmann constant, T is theabsolute temperature, q is the magnitude of charge of an electron, alsoreferred to as the elementary charge, and ∝ is an ideality factor. Thecurrent ratio of two diodes D1 (or DR) and D2 (or a selected one of thediodes D1-DN) is determined according to the following equation (2):

$\begin{matrix}{\frac{{ID}\; 1}{{ID}\; 2} = {\left( \frac{{AD}\; 1}{{AD}\; 2} \right)^{\frac{\Delta \; {VD}}{VT}}}} & (2)\end{matrix}$

where ID1 is the current through diode D1, ID2 is the current throughdiode D2, AD1 is the area of the diode D1, AD2 is the area of the diodeD2, and ΔVD is the difference of the diode voltages, or ΔVD=VD1-VD2. Itcan further be shown that the temperature T is determined according tothe following equation (3):

$\begin{matrix}{T = \frac{\left( \frac{\Delta \; {{VD} \cdot q}}{k} \right)}{\ln \; \left( \frac{{ID}\; {1 \cdot {AD}}\; 2}{{ID}\; {2 \cdot {AD}}\; 1} \right)}} & (3)\end{matrix}$

where “ln” denotes the natural logarithm. In this manner, T isproportional to the voltage difference and the ratios of the diode areasAD1 and AD2 and diode current ID1 and ID2.

The diode areas AD1 and AD2 and voltage difference ΔVD are predeterminedor otherwise known. In various embodiments, the currents between themultiple branches are matched by adjusting current mirror gain in onebranch so that the gain value difference is indicative of the relativecurrent between the two diodes. In one embodiment, a mapping isdetermined between gain values and temperature values, so that thetemperature may be determined using a corresponding gain value. In oneembodiment, a lookup table (LUT) or the like is generated or otherwiseprovided, in which a gain differential value is used as an index toretrieve a corresponding temperature value. In an alternativeembodiment, the temperature may be calculated or derived based on thegain differential value.

For both IDACs 308 and 325, a bit value of “1” pulls the gate of thecorresponding P-type FET high (e.g., to VDD) and turns the correspondingcurrent mirror leg off, whereas a bit value of “0” pulls the gate low(e.g., to COM) and turns it on. Each activated current mirror legincreases the gain of the current contributed to the common node 314.Thus, the digital values of O and G determine the current gain for eachcurrent mirror branch. As used herein, the “gain value” is considered inthe opposite sense as the corresponding digital value in which the gainvalue is increased when the digital value is decreased (more 0s) andvice-versa. Thus, each current mirror has highest gain when the IDACdigital value includes all zeroes and has lowest gain (or is off) whenthe IDAC digital value includes all ones.

It is noted that at least one current mirror leg should be activated foreach current mirror branch to allow at least a minimal amount of currentflow to node 314. In an alternative embodiment, at least one leg isplaced external to each IDAC 308 and 325 having its corresponding gateconnection pulled low so that the leg remains turned on to ensure atleast minimal current flow to node 314 for each current mirror branch.

In operation of the temperature measurement select and control system300, the controller 334 may perform an offset compensation procedureprior to each temperature measurement to minimize any offset between theIDACs 308 and 325. Also, offset compensation minimizes any offsetbetween the reference diode and the selected diode when in differencelocations. Next, the controller 334 performs a temperature measurementprocedure by adjusting circuit parameters including current mirror gain.Then the controller 334 uses the measured parameters, including the gaindifferential value, to retrieve, determine or otherwise calculate thetemperature value T.

The controller 334 first asserts SSEL to select a corresponding one ofthe site diodes D1-DN. The controller 334 asserts VSEL to assert thediode voltages VD1 and VD2 to the same voltage level and also outputsinitial digital values for the offset compensation value O and the gainvalue G. In one embodiment, the values of O and G are each initially setto the same “setpoint” value to initiate the offset calibrationprocedure. The setpoint value may be the midpoint of each IDAC 308 and325 to allow the O value to be adjusted up or down for offsetcompensation. Alternatively, the setpoint value is closer to one endbetween the minimum and maximum digital values of each of the IDACs 308and 325 to allow for a greater level of adjustment in the oppositedirection. For example, for a 128-bit configuration, the digitalmidpoint value is 64 which may be used as the setpoint. The digitalsetpoint may be positioned, however, closer to one end of the overalldigital range, such as the higher end for lower gain (e.g., 100), toallow sufficient headroom to adjust the O digital offset value higher orlower and then to allow a greater amount of room to reduce the digital Gvalue to increase gain.

While monitoring CX, the controller 334 adjusts the offset compensationdigital value O to determine the switch point of the comparator 318indicating a substantially equivalent current through each of thecurrent mirror branches (given the condition that VD1=VD2 for offsetcompensation). The digital G value remains at the initial setpoint. IfCX is high, then the gain of the compensation IDAC 308 is too high andthe gain of the IDAC 308 is reduced until CX switches low.Alternatively, if CX is low, then the gain of the compensation IDAC 308is too low and the gain of the IDAC 308 is increased until CX goes high.In either case, the adjusted value of the offset compensation value O atthe switching point of the comparator 318 minimizes any offsetdifferential between the current mirror branches while the IDAC 325 isprogrammed at the setpoint. In this manner the adjusted value of theoffset compensation value O minimizes discrepancies between the currentbranches.

After the offset compensation procedure is performed, the controller 334adjusts VSEL to control the voltage select block 302 to drive VD1 to areference voltage level and to drive VD2 to a delta voltage level toprovide a voltage difference ΔVD between the two voltages. In oneembodiment, the voltage level of VD2 is reduced while VD1 remains at thesame level that it was at during the offset compensation procedure. Inone embodiment, the reference voltage level is about 0.5V and the deltavoltage level is 0.45V for a difference voltage ΔVD of 0.05V. Theparticular voltage levels are arbitrary and may be adjusted fordifferent configurations. While monitoring CX, the controller 334 then“walks” the IDAC 325 by adjusting the gain value G until CX indicatesthe switch point of the comparator 318.

In one embodiment, the voltage of VD2 is reduced so that the currentthrough the IDAC 325 of the lower current mirror is reduced relative tothe upper reference current mirror and the CX value is pulled high. Inthis case, the gain value G is adjusted one bit at a time from theinitial setpoint to incrementally increase gain until the comparator 318switches state as indicated by CX being pulled low. The differencebetween the initial setpoint gain value and the final gain value whenthe comparator 318 switches state is indicative of the current ratiobetween the reference diode and the selected diode. The controller 334then uses the gain differential value to obtain a correspondingtemperature value T indicative of temperature.

In one embodiment, the controller 334 uses a memory, such as an LUT orthe like (see, e.g., LUT 1000 of FIG. 10), to retrieve the correspondingtemperature value. The gain differential value is applied as an index oraddress or the like into the memory to retrieve a correspondingtemperature value. In an alternative embodiment, the controller 334 isconfigured to convert the gain differential value to the current ratioID1/ID2, and to employ equation (3) or the like to calculate thetemperature value. As previously described, ΔVD and AD2/AD1 are bothknown (or otherwise determinable) so that temperature is a relativelysimple calculation. It is noted, however, that calculation circuitry mayprovide an unnecessary complication in favor of a simple and fast LUTconfiguration.

In an alternative embodiment, the compensation IDAC 308 is configured as(or otherwise replaced by) a static configuration. In one staticconfiguration embodiment, the offset compensation register 316 ispreprogrammed with the initial setpoint. In another staticconfiguration, the compensation register 316 is not provided and insteadthe gates of the P-type FETs of the array 312 are hardwired according tothe initial setpoint. In the static configuration, the P-type FETs ofthe arrays 310, 312, 326 and 328 may be configured as more preciselymatched devices to improve measurement. In the static configuration, theoffset compensation procedure may be bypassed or otherwise notperformed.

After a temperature measurement, the controller 334 may select the samesite or a different site by controlling SSEL and repeat the aboveprocess for making another temperature measurement.

FIG. 4 is a schematic and block diagram of a temperature measurementselect and control system 400 according to a VCO embodiment which may beused as the temperature measurement select and control block 102. Thetemperature measurement select and control system 400 is similar to thesystem 300 in which similar components are shown with the same referencedesignators. The voltage select block 302, the amplifiers 304 and 320,the reference diode DR, the devices N1, N2, P1 and P2, the IDACs 308 and325, and the MUX 324 for selecting one of the N diodes D1-DN areprovided and coupled to operate in similar manner.

The comparator 318 of the system 300 is replaced in the system 400 by aVCO 402 having an upper power node coupled to VDD and an outputproviding a frequency signal F. In this case, N4 is diode-coupled havingits gate coupled to its drain at node 314, which is further coupled tothe gates of additional N-type FETs N5 and N6. The drains of N5 and N6are both coupled to a lower power node 404 of the VCO 402. The source ofN5 is coupled to COM, and the source of N6 is coupled to the drain ofanother N-type FET SN1, having its source coupled to COM and its gatereceiving a switch signal SW1. It is noted that alternativeconfigurations for the VCO 402 and other VCOs described herein arecontemplated, such as coupling the lower power node (e.g., 404) toground or COM and coupling the upper power node to current mirroroutputs to achieve the same or similar results.

The drain and gate of diode-coupled N3 coupled at node 330 are furthercoupled to the gates of additional N-type FETs N7 and N8. The drains ofN7 and N8 are both coupled to the lower power node 404 of the VCO 402.The source of N7 is coupled to COM, and the source of N8 is coupled tothe drain of another N-type FET SN2, having its source coupled to COMand its gate receiving a switch signal SW2.

N5-N8 are marked with an “X” denoting that each of these devices has thesame size value, in which X denotes size or the relative amount ofcurrent that flows through the device when activated. SN1 and SN2 areboth relatively large devices which are configured to have substantiallyzero drain to source voltage when switched on to minimize its effect oncircuit operation.

The controller 334 is replaced by a similar controller 412 whichreceives the output frequency signal F from the VCO 402. The controller412 provides the VSEL, SSEL, G, O and T values in a similar manner, andfurther provides the switch signals SW1 and SW2. In one embodiment, thecontroller 412 incorporates a counter circuit or the like to measure theperiod of signal F in which the period is represented by a digital countvalue. A counter block 724 is illustrated in FIG. 7 for another VCOconfiguration although application is substantially similar.

The VCO 402 is shown implemented as a “ring oscillator” including anarray of 3 series-coupled inverter gates 406, 408 and 410 in which theoutput of the last inverter 410 is fed back to an input of the firstinverter 406. Each inverter has a positive supply voltage node coupledto node VDD and a negative power supply node coupled to the lower powernode 404. Each inverter 406, 408, 410 has its output coupled to an inputof the next inverter (forming a ring) and to one end of a correspondingcapacitor C1, C2 and C3, in which each capacitor C1-C3 has its other endcoupled to node 404. Each of the capacitors C1-C3 has a capacitancevalue which is independent of temperature. In one embodiment, forexample, each of the capacitors C1-C3 is implemented as a metalcapacitor that does not have a temperature coefficient.

The VCO 402 includes an odd number of inverters so that it oscillates ata frequency determined by the configuration of each of the inverters406-410, the capacitance of the capacitors C1-C3, and the averagecurrent provided between VDD and node 404 by the remaining currentmirror configuration. In one embodiment, the inverters and capacitorsare in a fixed configuration. Although 3 inverters and correspondingcapacitors are shown in the series-coupled configuration, it isunderstood that additional inverters and capacitors may be includeddepending upon the particular implementation.

The equation (3) provided above may be adjusted for the VCOconfigurations. The current of the VCO 402 is determined by itscapacitance, the voltage across it, and its frequency (or period) ofoscillation. The capacitors C1-C3 may be metal type capacitors or thelike with no temperature coefficient. As described further below, theprocess takes two different measurements providing two different periodsPER1 and PER2 of the F signal. The ratio of the periods is determined bythe ratio of the voltage differences, the ratio of the areas of thediodes, the voltage difference ΔVD and the thermal voltage VT. It can beshown that the temperature may be determined according to the followingequation (4):

$\begin{matrix}{T = \frac{\left( \frac{\Delta \; {{VD} \cdot q}}{k} \right)}{\ln\left( {\left( \frac{{PER}\; 1}{{PER}\; 2} \right)\sqrt{\frac{{ID}\; {1 \cdot \beta}\; 2}{\left( {{ID}\; {2 \cdot {\beta 1}}} \right) \cdot \left( \frac{{AD}\; 2}{{AD}\; 1} \right)}}} \right)}} & (4)\end{matrix}$

where β1 and β2 are the MOS transistor gain factors of the MOS devicesof the inverters 406, 408 and 410 of the VCO 402. The “beta” factors ortransistor gain factors are determined by channel carrier mobility, gateinsulator permittivity, gate insulator thickness, and the channeldimensions of the transistor devices. Although the beta factors areprocess dependent, they are both the same factor for the same VCO forthe two different measurements. Furthermore, they cancel each othersince provided in a ratio in equation (4).

As described further herein, the measurement process for the temperaturemeasurement select and control system 400 using the VCO 402 adjusts gainin a similar manner previously described between two differentmeasurements to equalize the frequency and thus the periods ofoscillation. In this manner, the resulting gain differential value maybe used in a similar manner previously described to obtain a temperaturevalue which is independent of circuit parameters including processvariations and source voltage. The temperature value may be obtainedusing a LUT or the like or may be calculated as previously described.

Operation of the temperature measurement select and control system 400is similar to that described for the temperature measurement select andcontrol system 300. The controller 412 performs an offset compensationprocedure prior to each temperature measurement to minimize any offsetbetween the IDACs 308 and 325. Next, the controller 412 performs atemperature measurement procedure by adjusting circuit parametersincluding current mirror gain. Then the controller 412 uses the gaindifferential value to determine the temperature value T indicative oftemperature. Again, a LUT or the like may be used, such as one similarto the LUT 1000. A primary difference of the system 400 compared to thesystem 300 is that the output frequency F of the VCO 402 is used as anindicator of the difference in current between the diode pair.

The controller 412 asserts SSEL to select a diode at a correspondingsite. The controller 412 then initiates the offset compensationprocedure by programming the G value of the IDAC 325 to the initialsetpoint value and by turning on the lower mirror configuration and byturning off the upper mirror configuration. In particular, thecontroller 412 asserts VSEL to set VD1 to 0V and to set VD2 to apredetermined higher voltage level (e.g., 0.5V). Furthermore, thecontroller 412 asserts SW1 to turn SN1 off and asserts SW2 to turn SN2on. The additional current path through N8 effectively doubles (2×) thecurrent through N7 applied to the VCO 402 for the lower current mirrorconfiguration to achieve a more accurate and balanced offsetcompensation value. The controller 412 allows F to settle and thenmeasures its period to obtain a baseline period value PER1.

The controller 412 then programs the O value of the compensation IDAC308 at the initial setpoint value and turns off the lower mirrorconfiguration and turns on the upper mirror configuration by assertingVSEL to set VD2 to 0V and to set VD1 to the predetermined higher voltagelevel. The G value remains at the initial setpoint value. Furthermore,the controller 412 asserts SW1 to turn SN1 on and asserts SW2 to turnSN2 off. Again, the additional current path through N6 effectivelydoubles (2×) the current through N5 applied to the VCO 402 for the uppercurrent mirror configuration to achieve a more accurate and balancedoffset compensation value. The controller 412 then monitors the periodof F while adjusting the digital O value of the compensation IDAC 308until the period of F is substantially equal to the baseline periodvalue PER1. In one embodiment, the controller 412 adjusts O one bit at atime, waits for F to settle, measures the new period of F, compares themeasured period with PER1, and determines whether additional adjustmentis necessary and if so, the direction of the correction either up ordown. When the new period of F substantially equals the baseline periodPER1, then offset compensation is complete.

The controller 412 then initiates a current measurement by asserting SW1and SW2 to turn both switches SN1 and SN2 off, and by asserting VSEL toadjust VD2 to the lower delta voltage level (e.g., 0.45V) to program thevoltage difference ΔVD between VD1 and VD2. Thus, VD1 is at thereference voltage level and VD2 is at the delta voltage level It isnoted that the current through N6 and N8 is turned off so that thecollective current through N5 and N6 is again about 2× what it otherwisewould be to obtain a balanced measurement. The controller 412 thenadjusts the digital G value from the initial setpoint until the newperiod PER2 of F is substantially equal to the reference period PER1. Inone embodiment, the controller 412 adjusts G one bit at a time, waitsfor F to settle, measures the new period of F, compares the measuredperiod PER2 with the reference period PER1, and determines whetheradditional adjustment is necessary. Since VD2 is less than VD1, the gainis typically increased to achieve a matching current level. When the newperiod PER2 of F substantially equals the baseline period PER1,adjustment of the gain value G is completed and a final gaindifferential value is obtained.

The controller 412 then uses the difference between the final gain valueand the initial setpoint gain value to determine the differential gainvalue indicative of the current ratio through the diodes. Thedifferential gain value may then be used to obtain the temperature valueT in a similar manner previously described.

The compensation IDAC 308 may be replaced by a static IDAC which ispreprogrammed or hardwired in a similar manner previously described. Forthe static configuration, the offset compensation procedure may bebypassed.

FIG. 5 is a schematic and block diagram of a temperature measurementselect and control system 500 according to another embodiment using apair of VCOs which may be used as the temperature measurement select andcontrol block 102. The temperature measurement select and control system500 has includes certain portions similar to the systems 300 and 400 inwhich similar components are shown with identical reference designators.The voltage select block 302, the amplifiers 304 and 320, the devicesN1, N2, P1, and P2, the MUX 324 and the diodes D1-DN are coupled tooperate in substantially similar manner. The IDACs 308 and 325 are alsoincluded and coupled in similar manner, except forming two separatecurrent mirror configurations with a corresponding pair of VCOs 502,shown individually as VCOs 1 and 2. Each of the VCOs 502 may beconfigured in substantially similar manner as the VCO 402 previouslydescribed, and each have upper power nodes coupled to VDD.

The compensation IDAC 308 is coupled between the drain and gate of P1and the drain and gate of N4 and receives the gain value O. N4 isdiode-coupled with its source coupled to COM and its drain and gatefurther coupled to the gate of an N-type FET N6. The source of N6 iscoupled to COM and its drain is coupled to the lower power node ofVCO 1. The primary IDAC 325 is coupled between the drain and gate of P2and the drain and gate of N3 and receives the gain value G. N3 isdiode-coupled with its source coupled to COM and its drain and gatefurther coupled to the gate of an N-type FET N5. The source of N5 iscoupled to COM and its drain is coupled to the lower power node of VCO2. VCO 1 outputs a first frequency signal F1 and VCO 2 outputs a secondfrequency signal F2. A controller 504 is provided, which receives F1 andF2 and which provides the select values VSEL and SSEL, the gain values Gand O, and the temperature value T.

In the illustrated embodiment of the system 500, the reference diode DRis replaced by N reference diodes DR1-DRN which are distributed with thediodes D1-DN, respectively. Thus, DR1 is co-located with D1, DR2 isco-located with D2, and so on. Another MUX 506 receives SSEL to selectthe corresponding co-located reference diode for each measurement. Theuse of the co-located reference diodes further reduces any error thatmay result from the pair of diodes not being located at the same site.The systems 300 and 400 may be modified accordingly in which the singlereference diode DR is replaced by the MUX 506 and the co-located diodesDR1-DRN.

The controller 504 asserts SSEL to select one of the diodes D1-DN and acorresponding one of the reference diodes DR1-DRN, asserts VSEL tocontrol the voltage select block 302 to control and apply the voltagesof VD1 and VD2, and asserts the O and G values to program the IDACs 308and 325 in substantially the same manner as previously described. Inthis case, however, the upper reference current mirror mirrors andamplifies current ID1 to drive the VCO 1 and the lower delta currentmirror mirrors and amplifies current ID2 to drive the VCO 2 to developfirst and second frequency signals F1 and F2 provided to the controller504.

In operation of the temperature measurement select and control system500, an offset compensation procedure is performed first followed by atemperature measurement procedure in a similar manner as previouslydescribed. For the offset compensation procedure, the controller 504provides VSEL so that VD1=VD2 and programs both of the IDACs 308 and 325with a predetermined setpoint value. The frequency signals F1 and F2should have about the same frequency level if the current mirrorbranches were configured in substantially similar manner.

The controller 504 adjusts the offset compensation value O whilemonitoring and comparing the periods of F1 and F2 until they are asclose as reasonably possible for offset compensation. The offsetcompensation adjusts for any offset discrepancies between the twocurrent mirror and VCO branches.

The controller 504 then adjusts VSEL so that VD2 is changed to the lowerdelta voltage level to develop the voltage difference ΔVD between VD1and VD2, in which VD1 remains at the reference voltage level. Thecontroller 504 then adjusts the gain value G from the initial setpointvalue while monitoring F1 and F2 until they are as close as reasonablypossible. The difference between the initial setpoint gain value and thefinal gain value of G determines the gain differential value which maythen be used to determine the temperature value T indicative oftemperature.

In an alternative configuration, after the offset compensationprocedure, the controller 504 adjusts VSEL so that VD2 is changed to thelower delta voltage level to develop the voltage difference ΔVD betweenVD1 and VD2 for the temperature measurement procedure. Rather thanfurther adjusting G, the controller 504 is configured to use the periodsbetween F1 and F2 when the voltage difference ΔVD is applied. Thedifference between the periods may be used to retrieve a correspondingtemperature value from an LUT or the like, or a temperature value may becalculated.

A difference between the temperature measurement select and controlsystems 400 and 500 is that system 500 uses two different VCOs formaking the measurement. It is noted, however, that the VCOs 502 areconfigured in substantially the same manner and process variations areeffectively canceled based on the ratio of beta values. Also, theco-located reference diodes may be used to improve temperaturemeasurement accuracy at the cost of additional components.

FIG. 6 is a schematic and block diagram of a temperature measurementsystem 600 implemented according to an alternative embodiment in which aportion of the temperature measurement select and control block 102 isinstead distributed with each of the thermal sensors 104. Thetemperature measurement system 600 includes a central temperaturecontrol block 602, select logic 604, and one or more local temperaturemeasurement networks 606 that are distributed at each location in whichtemperature is to be monitored and measured. A number N localtemperature measurement networks 606 are shown, numbered 1, . . . , N,each configured in substantially the same manner, each interfacing thecentral temperature control block 602 via the select logic 604.

The central temperature control block 602 shares a common set of signalswith any one of the local temperature measurement networks 606 whenselected by the select logic 604. In one embodiment, the common set ofsignals includes an IDAC bias voltage VID, an IDAC voltage level VDAC, abias voltage VB, a diode voltage VD, and a frequency signal F. Thecentral temperature control block 602 asserts a site select value SSELto select one of the local networks 606. The select logic 604 may beconfigured in any suitable manner, such as incorporating a switchmatrix, a bus structure, multiplexor logic, or the like for interfacingthe common signals between the central temperature control block 602 anda selected local network 606.

The central temperature control block 602 includes a controller 610, avoltage select block 612 (which operates in substantially the samemanner as the voltage select block 302 previously described), anamplifier 614, and an IDAC 616. The controller 610 asserts the SSELvalue to a select input of the select logic 604 for selecting one of thelocal temperature measurement networks 606. The controller 610 assertsVSEL to instruct the voltage select block 612 to assert the diodevoltage VD to the positive input of the amplifier 614. The output of theamplifier 614 provides the bias voltage VB to one terminal of the selectlogic 604 and has its negative input coupled to another terminal of theselect logic 604. The amplifier 614 operates in a similar manner aspreviously described to develop the VD voltage across the sensor diodeof a selected site, such as a diode D1 of the local temperaturemeasurement block 1 606. The controller 610 asserts a digital gain valueG to the IDAC 616, which provides a corresponding voltage VDAC toanother terminal of the select logic 604. The IDAC 616 also interfacesthe bias voltage VID, which is provided to another terminal of theselect logic 604. The controller 610 receives the frequency signal F atanother terminal of the select logic 604.

Further details of the local temperature measurement network 1 606 areshown, in which it is understood that each of the local temperaturemeasurement networks 606 are configured in substantially similar manner.The local temperature measurement network 1 includes N-type FETs N1-N5,P-type FETs P1-P5, the local diode D1 and a local VCO 622. The VCO 622may be configured in substantially similar manner as the VCO 402previously described. The voltage VD is provided to a node 620 which iscoupled to the anode of D1 and to the source of N1, in which the cathodeof D1 is coupled to COM. The gate of N1 receives the bias voltage VB andits drain is coupled to the drain and gate of P1 having its sourcecoupled to VDD. The gate of P1 is further coupled to the gates of P2 andP3, each having a source coupled to VDD. The drain of P3 is coupled tothe drain of P4 and to an upper power node of the VCO 622. The gate ofP4 receives the VDAC voltage and is further coupled to the gate of P5.The sources of P4 and P5 are coupled to VDD. The drain of P2 is coupledto the drain and gate of N2 and to the gate of N3. The drains of N3 andN4 are coupled together and to a lower power node of the VCO 622. Thegates of N4 and N5 are coupled together and to the drains of N5 and P5.The sources of N2-N5 are coupled to COM. The VCO 622 generates thefrequency signal F.

In operation of the temperature measurement system 600, when the localtemperature measurement network 1 is selected by the controller 610, theamplifier 614 controls N1 to maintain the VD voltage across D1, in whichD1 develops a diode current ID1. In this embodiment, a single diode isemployed for temperature measurement rather than a pair of diodes. Inthis case, the reference voltage level is first applied at a firstselected gain level to develop a reference current level for a firstreference period measurement, which is followed by application of thedelta voltage. The gain is adjusted until the new period matches thereference period to determine the gain differential value. P1-P3 andN2-N3 collectively operate to amplify and mirror the diode currentthrough the VCO 622. The controller 610 provides G to the IDAC 616,which asserts corresponding voltage level of VDAC to the localtemperature measurement network 1. P4-P5 and N4-N5 collectively operateto apply a corresponding current through the VCO 622.

The controller 610 asserts VSEL so that VD is at a first selectedreference voltage level and also asserts G at a selected level so thatthe IDAC 616 asserts VDAC at a corresponding voltage level. In oneembodiment, G is initially asserted at a predetermined setpoint leveland the controller 610 measures the corresponding period of F as areference period value PER1. The controller 610 then asserts VSEL tochange VD to the delta voltage level (e.g., the lower voltage value).While monitoring the period of F, the controller 610 then adjusts Guntil the period PER2 of F is substantially equal to the referenceperiod value PER1. In this manner, the difference between the initialand final gain values of G is indicative of the ratio of the current ID1for the two different voltage levels applied to the same diode. Thecontroller 610 then retrieves or calculates the temperature value Tindicative of temperature using the gain differential value in a similarmanner previously described.

The temperature measurement system 600 is similar to the systems 300 and400 in that the same VCO is used for measurement. The temperaturemeasurement system 600 is different in that a single diode is used forboth measurements rather than two different diodes. Also, theillustrated temperature measurement system 600 does not employ offsetcompensation. It is noted that offset issues are less problematic forthe system 600 since the same VCO, current mirror configuration anddiode are used for making the measurements.

FIG. 7 is a schematic and block diagram of a temperature measurementselect and control system 700 according to another embodiment withprogrammable parameters to expand the overall temperature range whichmay be used as the temperature measurement select and control block 102.A voltage select block 702 receives VSEL and provides a diode voltage VDin a similar manner as previously described. VD is provided to thepositive input of an amplifier 704, which has its output providing abias voltage VB to the gate of an N-type FET N2 and which has itsnegative input coupled to a node 705 which is further coupled to thesource of N1 in a similar manner previously described. Node 705 iscoupled to the output of a site select MUX 706 receiving site selectvalue SSEL for selecting a site for temperature measurement. In oneembodiment, each site has at least two diodes including a hightemperature range diode DH and a low temperature range diode DL. A rangeselect MUX 708 selects between the range diodes based on a range selectsignal RSEL.

The drain of N1 is coupled to a node 707, which is coupled to a firstprogrammable P-type mirror block PMIR 710. PMIR 710 is further coupledto a second programmable P-type mirror block PMIR 712. PMIR 710 isprogrammed with a gain value MA and PMIR 712 is programmed with a gainvalue MB. PMIR 712 is further coupled to a node 709 which is coupled tothe drain and gate of an N-type FET N2. An IDAC 714 receives a gainvalue G and is coupled to node 709. The source of N2 is coupled to COMand its gate and drain are further coupled to the gate of another N-typeFET N3. N3 has its source coupled to COM and its drain coupled to thelower power node of an VCO 716. The upper power node of the VCO 716 iscoupled to VDD and its output provides a frequency signal F. The VCO 716may be configured in substantially similar manner as the VCO 402previously described.

The temperature measurement select and control system 700 furtherincludes a controller 720, which further includes an oscillationdetector 722, a counter block 724, a temperature control block 726, anda memory 728. The oscillation detector 722 receives F at its input andprovides a frequency signal FR at its output to the input of the counterblock 724. The counter block 724 has an output providing a period valuePER to the input of the temperature control block 726. The temperaturecontrol block 726 asserts the VSEL, SSEL and RSEL select values alongwith the gain values MA, MB and G, and receives the PER signalindicative of the period of F. The temperature control block 726 isconfigured to convert one or more each of the gain value(s) G and thecorresponding PER values for determining and providing the temperaturevalue T. As further described below, the memory 728 stores tabularvalues used for mode selection and includes at least one look-up table(LUT) for converting digital gain values to corresponding temperaturevalues T.

As understood by the relationships previously described, the current ofa forward-biased PN junction (e.g., diode) changes exponentially so thatthe temperature measurement range may potentially be limited to within a30-40 degree temperature range with a static configuration. The system700 is configured with multiple configuration modes for accuratelymeasuring temperature within a relatively wide temperature range. Eachconfiguration mode has a different device size, a different “effective”device size, and different diode voltages which are collectivelyoptimized for a different temperature range. Logic control manages thetransition among the modes based on measurement parameters indicative ofthe ambient temperature.

The size or area of the activated diode determines the device size. Thediode DH has a size associated with higher temperature ranges and thediode DL has a different size which is associated with lower temperatureranges. In one embodiment, for example, the diode DH is smaller so thatit develops a lower current for application of a given voltage levelwhich is suitable for higher temperature ranges, whereas the diode DL islarger so that it develops a higher current for application of the samevoltage level which is suitable for lower temperature ranges. PMIR 710and PMIR 712 form a portion of the current mirror configuration withprogrammable mode gain in which each mode corresponds with a temperaturesubrange. Thus, the combination of gain values MA and MB determine themode gain of the current mirror configuration thereby programming theeffective device size. In one embodiment, for example, lower gain valuesresult in lower current levels suitable for the higher temperatureranges, whereas higher gain values result in higher current levelssuitable for the lower temperature ranges.

The use of the two programmable current mirror blocks PMIR 710 and 712provides flexibility to achieve a desired temperature range and accuracylevel for temperature measurements for each mode. In an alternativeembodiment, only one of the blocks is programmable, in which theprogrammable block has an increased size to provide desired range andaccuracy or otherwise may be used for configurations with reduced rangeor accuracy. N2 and N3 provide the N-type portion of the current mirrorconfiguration. In alternative embodiments, either or both of the N2 andN3 devices may be replaced with corresponding programmable gain blocksin a similar manner as the PMIR blocks for increased range or accuracy.

The voltage select block 702 provides at least two different voltagelevels (e.g., VDH and VDL) to measure temperature within eachtemperature subrange. In one embodiment, for example, the VDH and VDLvalues are lower to develop reduced current levels for the highertemperature ranges, whereas the VDH and VDL values are higher to developincrease current levels for the lower temperature ranges. In oneembodiment, VDH provides the reference voltage level and VDL providesthe delta voltage range for a given temperature subrange.

Operation of the temperature measurement select and control system 700as controlled by the controller 720 is similar to that previouslydescribed for the alternative embodiments for each temperature subrange.Current developed through a selected diode is mirrored and amplified todevelop a corresponding operating voltage of the VCO 716, which outputsF at a corresponding frequency level. The gain value G provides a searchgain which is adjusted within each temperature range while monitoringthe periods of F to search for the actual temperature. The temperaturecontrol block 726 asserts SSEL to select a site for temperaturemeasurement, and further asserts the RSEL value and the MA and MB modegain values for a selected temperature range. The temperature controlblock 726 then asserts VSEL for the corresponding diode voltages andadjusts the gain value G provided to the IDAC 714 to measure temperaturewithin the selected range. If the gain value G of the IDAC 714 goes outof range during the measurement, then the actual temperature is notwithin the selected range and a new temperature range is selected.

In one embodiment, the overall temperature range is about 0° C.(Celsius) to about 125° C., which is further subdivided into temperaturesubranges 0-40° C., 40-70° C., 70-100° C., and 100-125° C. It is notedthat the settings for the lower temperature subranges may result inexcessively high current if the actual ambient temperature is high.Thus, if the system parameters are set for low temperature rangemeasurement when the actual temperature is significantly higher,excessive currents may cause over-current conditions which may furthercause malfunction or even catastrophic failure of one or more devices orcomponents. In this manner, temperature measurement search issuccessively performed from the higher temperature subranges towards thelower temperature subranges to ensure circuit operation reliability.

It is noted that if the actual temperature is low when the temperaturemeasurement search is performed at a higher temperature subrange, thenthe resulting current may be too low to develop sufficient voltage tooperate the VCO 716. Thus, the VCO 716 may fail to oscillate which mightotherwise cause a misreading and/or a non-reading by the counter block724. The oscillation detector 722 determines whether the F signal isoscillating and asserts FR accordingly. If the oscillation detector 722determines that F is oscillating, it passes the F signal unmodified asthe FR signal. If, however, the oscillation detector 722 determines thatF is not oscillating, then the oscillation detector 722 generates arelatively low frequency of FR to drive the counter block 724. Thecounter block 724 measures the period of FR and provides a correspondingcount value PER to the temperature control block 726. If the temperaturecontrol block 726 detects PER above an expected range indicatingnon-oscillation of F, then it selects the next lower temperaturesubrange for measurement.

FIG. 8 is a schematic diagram of an exemplary embodiment of the PMIR 710coupled to an exemplary embodiment of the PMIR 712 according to oneembodiment. The PMIR 710 includes a first array of an integer number Jof P-type FETs 802 and a second array of J P-type FETs 804. Each P-typeFET of the first array 802 has its gate and drain coupled to node 707,and its source coupled to the drain of a corresponding one of the P-typeFETs of the second array 804. The source of each P-type FET of thesecond array 804 is coupled to VDD. The gate of each P-type FET of thesecond array 804 receives a corresponding bit of the digital mode gainvalue MA, shown as MA₁, MA₂, . . . , MA_(T).

The PMIR 712 is configured in substantially similar manner. The PMIR 712includes a first array of an integer number K of P-type FETs 806 and asecond array of J P-type FETs 808. Each P-type FET of the first array802 has its drain coupled to node 709, its gate coupled to node 707, andits source coupled to the drain of a corresponding one of the P-typeFETs of the second array 808. The source of each P-type FET of thesecond array 808 is coupled to VDD. The gate of each P-type FET of thesecond array 808 receives a corresponding bit of the digital mode gainvalue MB, shown as MB₁, MB₂, . . . , MB_(K).

Each bit of the gain values MA or MB turns on or off a corresponding legof the array of P-type FETs to adjust the mode gain of the currentmirror. When pulled high, the current mirror leg is turned off reducingcurrent gain, and when pulled low, the current mirror leg is turned onincreasing current gain. The use of both PMIR blocks 710 and 712 allowsrefinement of mode gain adjustment for more accurate temperaturesubrange selection.

The IDAC 714 may be implemented in a similar manner as the PMIR 712. Aspreviously described, the IDAC 714 provides a search gain which isprogrammable and adjusted during each temperature measure search tosearch for the actual temperature within a selected temperature range.

FIG. 9 is a diagram of a temperature range mode select table 900 thatmay be stored within the memory 728 and which includes the values tofacilitate mode selection for each of the predetermined temperaturesubranges. Each temperature subrange has corresponding reference (e.g.,upper) and delta (e.g., lower) diode voltages for VD, a selected one ofthe diodes DH and DL determined by the temperature range RSEL value,corresponding mode gain values for MA and MB for programming the PMIR710 and 712 for each temperature subrange, and at least one IDACreference (DAC_REF) value as the initial gain value G for programmingthe IDAC 714. These values are determined based on a variety of factorsand may further be determined empirically. In general, the values areselected to optimize the circuitry for accuracy of the temperaturesearch within each temperature subrange.

For the upper subrange of 100-125° C., the VD, RSEL, MA, MB and DAC_REFvalues are VH1 & VL1, DH, MA1, MB1, and SP1₁-SP1₄, respectively. For thenext higher range of 70-100° C., the VD, RSEL, MA, MB and DAC_REF valuesare VH2 & VL2, DH, MA2, MB2, and SP 2₁-SP 2₄, respectively. For the nexttemperature range of 40-70° C., the VD, RSEL, MA, MB and DAC_REF valuesare VH3 & VL3, DL, MA3, MB3, and SP 3₁-SP 3₄, respectively. For thelowest temperature range of 0-40° C., the VD, RSEL, MA, MB and DAC_REFvalues are VH4 & VL4, DL, MA4, MB4, and SP 4₁-SP 4₄, respectively.

The DAC_REF values are the initial values of G programmed into the IDAC714 as an initial reference value during temperature measurement. Theillustrated embodiment shows four DAC_REF values for each temperaturesubrange. In this case, each subrange may be further divided into fournarrower temperature windows in which each window corresponds with oneof the different DAC_REF reference values. The DAC_REF values may bedetermined during a calibration procedure, and may further be usedduring a temperature measurement procedure. During the calibrationprocedure, the temperature is known and an initial DAC_REF value is usedas a reference point for a corresponding gain value for thattemperature. Once the actual gain value is obtained, the DAC_REF valuemay be updated and the process repeated to achieve greater accuracy.

During the temperature measurement procedure, since the temperature isnot initially known, a default value or one of the stored DAC_REF valuesare initially used for an initial temperature measurement. Once aninitial temperature value is determined, the DAC_REF value for thecorresponding temperature window range may be selected and thetemperature procedure is repeated for a more accurate measurement. Inalternative embodiments, more or less than four DAC_REF values arestored. In one embodiment, DAC_REF values are not stored and a defaultDAC_REF value is used.

FIG. 10 is a diagram of a temperature versus gain lookup table (LUT)1000 which may be stored within the memory 728 and which lists an IDACgain differential value (or simply, gain value) for selected temperaturevalues within each temperature subrange of the overall temperaturerange. The overall temperature range (e.g., 0-125) is subdivided intofour different temperature subranges denoted by a subrange index. Asshown, index 1 corresponds with temperature subrange 100-125° C., index2 corresponds with temperature subrange 70-100° C., index 3 correspondswith temperature subrange 40-70° C., and index 4 corresponds withtemperature subrange 0-40° C. In the illustrated embodiment, theselected temperatures within each subrange are separated by 4 degreeincrements rather than providing a gain value for each degree oftemperature. Each listed temperature value corresponds with a gain valueof the IDAC 714 in the form GI_(TEMP), in which “I” denotes the subrangeindex and “TEMP” denotes the temperature in ° C. For example, a gainvalue G2₇₀ denotes an IDAC gain value G which corresponds with 70° C.within the temperate subrange index of 2 (70-100).

Alternative embodiments are contemplated in which the separation is moreor less than 4 degrees, such as, for example, separation by only one ortwo degrees or five degrees or greater. 4 degree separation providessufficient accuracy while reducing memory consumption as compared toproviding a gain value for each degree of temperature. Intermediatetemperature values may be interpolated by interpolating gain values asfurther described herein. Furthermore, the temperature ranges overlapeach other to reduce possible misreading. As shown, the highesttemperature of 128° C. of the first temperature subrange (index 1) isslightly greater than the target temperature range maximum of 125° C.Furthermore, each subsequent temperature subrange overlaps thepreviously higher temperature subrange by an overlap amount, such as bysix degrees (6° C.). As shown, for example, the highest temperature ofthe second temperature subrange (index 2) is 106° C. which is greaterthan the lowest temperature (100° C.) of the first temperature subrange(index 1) by 6° C.

As described further herein, a calibration procedure is performed toprogram each lookup table for a given configuration, which may be asingle lookup table for all sites or a separate lookup table for eachsite. During the calibration procedure, the external ambient temperatureis controlled to a selected temperature corresponding with the lookuptable, and a corresponding gain value is determined for that temperatureand stored. During temperature measurement, each temperature subrange issearched one at a time from the higher temperature subrange to thelowest temperature subrange for a given site until a valid and finalgain value is determined. The corresponding lookup table is referencedto retrieve a corresponding temperature, or to retrieve temperaturevalues and corresponding gain values on either side of the measured gainvalue. The temperature may then be interpolated based on the retrievedgain and temperature values.

FIG. 11 is a simplified block diagram of the oscillation detector 722according to one embodiment. A free-running oscillator 1102 provides alow frequency signal LF to one input of an analog MUX 1104, whichreceives the F signal at its other input. F is also provided to an inputof an oscillation detection block 1106, and the output of the MUX 1104provides the FR signal. The oscillation detection block 1106 asserts aselect signal SEL to a select input S of the MUX 1104. In theillustrated embodiment, LF is provides to the “0” input of MUX 1104 andF is provided to the “1” input of the MUX 1104, in which “0” and “1”reflect the logic value of the SEL signal.

The oscillation detection block 1106 continuously, or periodically,monitors F for oscillation. When F is detected as oscillating, theoscillation detection block 1106 asserts SEL to select F as the outputFR. When F is not oscillating, the oscillation detection block 1106asserts SEL to select LF as the output FR. As previously noted, LFprovides a sufficient clock signal for operating the counter block 724to provide a count value PER at its output. When LF is selected as theFR signal, PER has a relatively low value indicating non-oscillation ofF.

FIG. 12 is a flowchart diagram of a calibration procedure according toone embodiment which may be performed by the system 700 for determiningand storing gain values corresponding to temperature values. Theelectronic system 100 is located within a controlled temperatureenvironment and the ambient temperature is externally controlled. At afirst block 1202, the temperature (e.g., ambient temperature) iscontrolled to a particular temperature value which corresponds with thetemperature values in the temperature lookup table, such as the LUT1000. In one embodiment, the temperature may be initialized at one endof the overall temperature range (e.g., the lower end at 0° C.), andthen adjusted (e.g., increased) at a selected rate (e.g., gradual rate)towards the opposite end. When the temperature reaches a valuecorresponding to an entry in the corresponding temperature lookup table,a calibration process may be performed for that temperature level.

At next block 1204, a site is selected by assertion of the SSEL value inthe event that multiple sites are provided. This step may be omitted orbypassed when there is only one site. At next block 1206, the modeparameters that correspond with the temperature subrange of the actualtemperature are applied. As an example, for the temperature measurementselect and control system 700, the temperature sensor device size, theeffective device size, and the initial diode voltage are programmed forthe temperature subrange which corresponds with the actual temperature.As shown in table 900, for example, when the temperature is 0° C. withinthe first subrange of 0-40° C., the initial diode voltage is VD=VH4 (thereference voltage value for the lowest temperature subrange) controlledby VSEL, the initial device size is DL selected by RSEL, and the modegain values MA4 and MB4 are selected and applied to the PMIR 710 and712, respectively.

At next block 1208, an initial DAC reference value DAC_REF is selectedas the gain value G and the IDAC 714 is programmed accordingly. TheDAC_REF value may be stored in the memory 728 or may be a predetermineddefault value or the like. DAC_REF serves as a reference search gainvalue. At next block 1210, the period of the output frequency F of theVCO 716 is measured, which corresponds with a reference period PER1.

Operation then proceeds to next block 1212 to initiate the temperaturesearch mode in which the diode voltage is changed to the delta voltagevalue, such as a lower diode voltage VD. As shown in table 900, forexample, when the temperature is 0° C. within the first subrange of0-40° C., the diode voltage is changed to VD=VL4 (the delta voltagevalue for the lowest temperature subrange) selected by VSEL. The changeof diode voltage changes the diode current to a delta current level,which correspondingly changes the frequency of signal F at the output ofthe VCO 716. At next block 1214, the search gain value G is changed toan initial search value for the temperature search and programmed intothe IDAC 714. At next block 1216, the period of the output frequency Fof the VCO 716 is measured and a measured delta period PER2 is updatedaccordingly. At next block 1218, it is queried whether the reference anddelta periods PER1 and PER2 are equal. If not, operation proceeds toblock 1220 to determine whether additional gain adjustments are to bemade to the IDAC 714, and if so, operation proceeds to block 1222 toadjust the gain of the IDAC 714. Operation then loops back to block 1216to measure the period of F again to update PER2 to a new value.Operation loops between blocks 1216 and 1222 until PER1 and PER2 areequal or until it is determined that there are no further gainadjustments.

It is appreciated that various different methods may be used toimplement gain adjustment and comparison as represented by the loopbetween blocks 1216 and 1222. It is noted that in a practicalconfiguration, the resolution of the IDAC 714 may not be sufficientlyhigh to ensure that the reference and value periods exactly match eachother, so that the inquiry of block 1218 may often return false. Block1218 may be modified to inquire whether the period values are within apredetermined tolerance level of each other. Alternatively, the searchmethod is configured to determine the gain value that provides theclosest match.

In one embodiment, a binary search method is performed to identify theclosest match. The initial search value applied at block 1214 may havean initial value which is approximately in the middle of an initialsearch range. The initial search range may be, for example, the minimum(MIN GAIN) and maximum (MAX GAIN) gain values of the IDAC 714, in whichthe initial search value is the middle gain value MID GAIN determined asMID GAIN=(MIN GAIN+MAX GAIN)/2. If the period values do not match usingMID GAIN, then block 1220 queries whether the frequency of F should beincreased or decreased and a new, reduced search range is determined.For example, the new search range is the upper half of the originalsearch range if the frequency should be increased (by setting MIN GAINequal to MID GAIN), or the lower half of the search range if thefrequency should be decreased (by setting MAX GAIN equal to MID GAIN).The MIN GAIN or the MAX GAIN value is adjusted accordingly, and a newMID GAIN value is determined at block 1222 using the same formulationMID GAIN=(MIN GAIN+MAX GAIN)/2, and evaluated at block 1216. Operationrepeats until a final gain value is determined at either block 1218(when equal) or block 1220 (when closest gain value determined or whenno additional adjustments may be made).

As an example, assume that the IDAC 714 is 128 bits for a minimum valueof 1 and a maximum value of 128 with a first MID GAIN value of 64. Alsoassume that the closest gain value is 86. At 64, PER1 and PER2 are notequal and PER1>PER2, so that the new range is between 64 and 128 with anupdated MID GAIN value of 96. At 96, PER1 and PER2 are not equal andPER2<PER1, so that the new range is between 64 and 96 with an updatedMID GAIN value of 80. At 80, PER1 and PER2 are not equal and PER2>PER1,so that the new range is between 80 and 96 with an updated MID GAINvalue of 88. At 88, PER1 and PER2 are not equal and PER2<PER1, so thatthe new range is between 80 and 88 with an updated MID GAIN value of 84.At 84, PER1 and PER2 are not equal and PER2>PER1, so that the new rangeis between 84 and 88 with an updated MID GAIN value of 86. If PER1 andPER2 are equal as determined at block 1218, then the closest gain valuehas been determined as 86.

Although 86 is the closest value, it is possible, and even likely, thatPER1 and PER2 are not equal as determined at block 1218. In this case,based on the comparison between PER1 and PER2, the final MID GAIN valueis either 87 or 85. At this point, no further gain adjustments arenecessary since narrowed down to only two values. In one embodiment, thefinal MID GAIN value of either 87 or 85 is accepted allowing for lessthan 1 degree of error. Alternatively, one or more of the period valuescorresponding to the determined PER2 values are temporarily stored andcompared to identify the closest gain value, such as 86 in thisparticular example.

Alternative methods are contemplated, such as, for example, simplywalking the IDAC 714 from its lowest gain value towards the highest gainvalue, or vice-versa, while comparing each PER2 period value to identifythe closest gain value.

When either PER1=PER2 or there are no further gain adjustments to test,operation proceeds to block 1224 in which the gain differential value isdetermined and stored in the corresponding lookup table (e.g., LUT 1000)for a corresponding temperature value for the corresponding temperaturesubrange. The gain differential value is determined as the differencebetween the initial DAC_REF value and the final gain value of G. If theDAC_REF value is equivalent to a minimum gain value (e.g., gain of 0 or1), then the final gain value may be stored instead. Operation may thenproceed to block 1226 to inquire whether a different temperaturesubrange should be tested for the current temperature. As illustrated byLUT 1000, for example, there may be overlapping temperature valueswithin different temperature subranges (e.g., temperature 40° C. isprovided in both of the lower temperature subranges). If so, operationreturns to block 1206 in which the parameters for the differenttemperature subrange are applied, and operation repeats for the currenttemperature within the new temperature subrange.

Otherwise, operation proceeds to block 1228 to inquire whether adifferent site should be tested for the current temperature. When thereare multiple sites, each site may be tested at the current temperature.If so, operation returns to block 1204 to select a different site.

Otherwise, operation proceeds to block 1230 to determine whetheradditional temperatures need to be tested. If so, operation returns toblock 1202 in which a new temperature is applied. Once the temperature0° C. is tested, for example, the temperature may be increased to 4° C.and the entire process repeated for the new temperature until thecorresponding one or more lookup tables are completed. Otherwise,operation is completed.

The calibration procedure illustrated by the flowchart of FIG. 12 isexemplary only and may be modified for different configurations. Also,the calibration procedure may be modified to determine more accurateDAC_REF values for temperature window ranges within each temperaturesubrange to potentially achieve greater accuracy.

FIG. 13 is a flowchart diagram of a temperature measurement procedureaccording to one embodiment which may be performed by the system 700 formeasuring temperature. In this case the electronic system 100 isoperating and it is desired to measure and monitor the temperature atone or more sites. The temperature measurement procedure issubstantially similar to the calibration procedure except that thetemperature is not controlled and is otherwise unknown. At first block1302, a site is selected by assertion of the SSEL value in the eventthat multiple sites are provided. This step is omitted or bypassed whenthere is only one site. At next block 1304, the parameters thatcorrespond with the “next” temperature subrange are applied. In thefirst iteration in order to avoid possible failure, the highesttemperature subrange is presumed. As an example, for the temperaturemeasurement select and control system 700, the temperature sensor devicesize, the effective device size, and the reference diode voltage areprogrammed for the highest temperature subrange. As shown in table 900,for example, the initial diode voltage is VD=VH1 (the reference voltagevalue for the highest temperature subrange) selected by VSEL, theinitial device size is DH selected by RSEL, and the gain values MA1 andMB1 are selected and applied to the PMIR 710 and 712, respectively.

At next block 1306, an initial or default DAC_REF is selected as thegain value G and the IDAC 714 is programmed accordingly. The initial ordefault DAC_REF may be stored in the memory 728 or may be apredetermined default value or the like. Although one of the DAC_REFvalues from the table 900 may be used, the temperate is yet unknown inthe first iteration so that one may be arbitrarily selected. When thefinal temperature value is determined, the corresponding DAC_REF valuefrom the table 900 may be retrieved and the temperature measurementprocedure repeated using the retrieved DAC_REF value to potentiallyobtain a more accurate temperature measurement.

At next block 1308, the period of the output frequency F of the VCO 716is measured, which corresponds with a reference period PER1. Aspreviously noted, however, it is possible that the VCO 716 is unable tooscillate in the event the driving current and voltage levels are toolow, such as when the temperature is low and a high temperature subrangeis assumed. In this case, operation proceeds to block 1310 to inquire asto whether the VCO 716 is oscillating. This determination may be made bydetermining whether the period corresponds with a high period valuePER_HI in which the oscillation detector 722 has detectednon-oscillation. If the VCO 716 is not oscillating, then operationreturns to block 1304 in which the next lower temperature subrange isselected.

If there is oscillation as determined at block 1310, then operationproceeds to block 1312 to initiate the temperature search mode in whichthe diode voltage is changed to a different value, such as a delta(lower) VD diode voltage. As shown in table 900, for example, for thehighest temperature subrange of 100-125° C., the diode voltage ischanged to VD=VL1 (the delta voltage value for the highest temperaturesubrange) selected by VSEL. The change of diode voltage changes thediode current to a new level, which correspondingly changes thefrequency of signal F at the output of the VCO 716.

At next block 1314, the gain value G is changed to an initial searchvalue for the temperature search and programmed into the IDAC 714. Atnext block 1316, the period of the output frequency F of the VCO 716 ismeasured and the PER2 value is updated accordingly. At next block 1318,it is once again queried whether there is oscillation. Althoughoscillation was verified at block 1310, it may have been under marginalconditions and the parameters have changed. If there is no oscillation,operation returns to block 1304 to advance to the next lower temperaturesubrange. If there is oscillation, operation proceeds to block 1320 inwhich it is queried whether the reference and delta periods PER1 andPER2 are equal. If not, operation proceeds to block 1322 to determinewhether additional gain adjustments are to be made to the IDAC 714, andif so, operation proceeds to block 1324 to adjust the gain of the IDAC714. Operation then loops back to block 1316 to measure the period of Fagain to update PER2 to a new value.

In a similar manner as described above for the calibration procedure,operation loops between blocks 1316 and 1324 until PER2 and PER1 areequal or until it is determined that there are no further gainadjustments. As noted above, various methods may be used to implementgain adjustment and comparison, such as a binary or linear search or thelike. The binary search method provides a quick and efficient means forconverging on the gain value corresponding with the actual temperature.If PER1 and PER2 are not equal and no further adjustments of gain areavailable as determined at block 1322, then operation proceeds to block1326 to inquire whether the IDAC 714 has reached one of its limits, suchas its lowest limit value. If so, then the selected temperature subrangeis too high and operation returns to block 1304 to advance to repeat thesearch within the next lower temperature subrange.

When PER2=PER1, or if there are no further gain adjustments and the IDAC714 has not reached a limit value, then operation proceeds to block 1328in which the gain differential value is determined and used to retrievea corresponding temperature value from the corresponding lookup table,such as the LUT 1000. The gain differential value was determined as thedifference between the final gain value and the DAC_REF value. Thereference period PER1 was determined using DAC_REF as the gain withapplication of the reference voltage level applied to the selecteddiode, and the new period PER2 was determined using the final gain valueof G with application of the delta voltage level applied to the thermalsense diode. Thus the gain differential value indicates the ratio ofdiode current resulting from application of the reference versus thedelta voltage level. Alternatively, if the DAC_REF value is equivalentto a minimum gain value, then the final gain value may be used as thegain differential value.

It is noted that it is possible, maybe even likely, that the exact gainvalue is not directly listed in the lookup table. As shown in the LUT1000, for example, the temperature values are separated by 4° C.increments so that the gain values are spread accordingly. Thecorresponding temperature may be determined by interpolation. First, thegain values in the lookup table above and below the measured gain valueare determined and retrieved along with the corresponding temperaturevalues. The measure gain value is interpolated between the retrievedgain values and a temperature is interpolated between the correspondingretrieved temperature values in a linear manner. For example weightingvalues may be applied to the retrieved temperature values to interpolatea final temperature value.

Operation then proceeds to block 1330 in which the subrange is advancedback to the highest (or next higher) temperature subrange for making asubsequent measurement at the same site or at a different site. Althoughthe temperature may not have changed by a significant degree, oneapproach is to return back to the highest subrange for any subsequentmeasurement.

In an alternative embodiment, rather than returning to the highestsubrange, operation returns to the next higher subrange since thetemperature is unlikely to change by a significant amount betweensuccessive measurements. With reference to LUT 1000, for example, if thetemperature is determined as 42° C. within the third subrange 40-70° C.,then the subrange may be changed to the next higher subrange 70-100° C.for a potentially faster temperature search.

Operation then proceeds to block 1332 in which it is queried whether tomake another measurement at the current site selection. If so, operationreturns to block 1304 in which the parameters for the selectedtemperature subrange (e.g., current, highest, or next higher) andoperation continues for another measurement. If another measurement isnot to be made at the current site, operation proceeds to block 1334 toinquire whether to make a measurement at a different site. If so,operation returns to block 1302 to select a different site. Otherwise,operation is completed.

The reference and delta voltages may be configured for particularprocess technologies and target temperature ranges among other factorsand variables. Many types of process technologies are contemplated, suchas, for a non-limiting list of examples, 90 nanometer (nm), 40 nm, 28nm, 20 nm, 14 nm, etc. The thermal sensor sizes and applied biasvoltages may be varied or otherwise adjusted based on the processtechnology and other circuit parameters. In one non-limiting specificembodiment using 28 nm technology, for example, a reference voltage ofabout 0.5V and a delta voltage of about 0.45V with a voltage differenceof 0.05V, or 50 millivolts (mV) may be used for the highest temperaturesubrange of 100-125° C. In the same specific embodiment, the voltagesare adjusted upwards to a reference voltage of about 0.8V and a deltavoltage of about 0.75V with a voltage difference of 50 mV. The voltagedifference may may be the same or may be adjusted for each temperaturesubrange. In general, the reference and delta temperatures may have anysuitable voltage levels depending upon the particular processimplementation. For existing process technologies, the voltage levelsrange from about 100 mV up to about 1V with a difference voltage rangingbetween a few mV (e.g., 20 mV) up to a few hundred mV (e.g., 200 mV).

Although the invention is described herein with reference to specificembodiments, various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. In alternative configurations, for example, inverse sourcereference and/or circuitry may be implemented relative to the sourcevoltages while achieving the same or similar results. For example, thethermal sensing diodes (e.g., DR, D1, D2, DN, etc.) are shown havingcathodes referenced to a ground or COM but instead may have their anodescoupled to a source voltage, such as VDD or the like, in which thesupporting circuitry is changed accordingly to achieve similar results.Similarly, The VCOs (e.g., 402, 502, 622, 716) are shown having an upperpower node coupled to VDD, whereas alternative configurations arecontemplated in which the lower power nodes are instead referenced to aground or COM and the current mirror configuration develops a voltage ontheir corresponding upper power nodes to achieve similar results.

Accordingly, the specification and figures are to be regarded in anillustrative rather than a restrictive sense, and all such modificationsare intended to be included within the scope of the present invention.Any benefits, advantages, or solutions to problems that are describedherein with regard to specific embodiments are not intended to beconstrued as a critical, required, or essential feature or element ofany or all the claims. Unless stated otherwise, terms such as “first”and “second” are used to arbitrarily distinguish between the elementssuch terms describe. Thus, these terms are not necessarily intended toindicate temporal or other prioritization of such elements.

1. A thermal sensor system, comprising: at least one thermal sensor; avoltage control network which applies a reference voltage level and adelta voltage level to said at least one thermal sensor, wherein said atleast one thermal sensor develops a reference current signal in responseto said reference voltage level and a delta current signal in responseto said delta voltage level; a current gain network configured to adjustgain of said delta current signal relative to said reference currentsignal; a current compare sensor responsive to said reference currentsignal and said delta current signal which is configured to provide acomparison metric; and a controller which is configured to control saidcurrent gain network to adjust gain of said delta current signal whilemonitoring said comparison metric to determine a gain differential valueindicative of a current ratio of said reference current signal and saiddelta current signal, wherein said controller determines a temperaturevalue based on said gain differential value.
 2. The thermal sensorsystem of claim 1, wherein said at least one thermal sensor comprises atleast one diode.
 3. The thermal sensor system of claim 1, wherein: saidat least one thermal sensor comprises first and second thermal sensors;wherein said voltage control network comprises a first amplifier whichapplies said reference voltage level to said first thermal sensor and asecond amplifier which applies said delta voltage level to said secondthermal sensor; and wherein said current gain network comprises a firstprogrammable current mirror which adjusts gain of said delta currentsignal.
 4. The thermal sensor system of claim 3, wherein said currentgain network further comprises a second programmable current mirrorwhich applies an offset compensation gain to said reference currentsignal.
 5. The thermal sensor system of claim 1, wherein said currentgain network comprises: at least one current mirror which mirrors saidreference current signal and said delta current signal; and aprogrammable gain block which applies a programmed gain to said deltacurrent signal.
 6. The thermal sensor system of claim 1, wherein saidcurrent compare sensor comprises a comparator responsive to adifferential between said reference current signal and said deltacurrent signal.
 7. The thermal sensor system of claim 1, wherein saidcurrent compare sensor comprises at least one voltage controlledoscillator responsive said reference current signal and delta currentsignal.
 8. The thermal sensor system of claim 1, further comprising:said at least one thermal sensor comprising a plurality of distributedthermal sensors; and select logic configured to select at least one ofsaid plurality of distributed thermal sensors for temperaturemeasurement.
 9. The thermal sensor system of claim 8, wherein: saidplurality of distributed thermal sensors comprises a plurality ofdistributed reference thermal sensors and a plurality of delta thermalsensors; and wherein said select logic is configured to select aco-located pair of said plurality of distributed reference thermalsensors and said plurality of delta thermal sensors for each temperaturemeasurement.
 10. The thermal sensor system of claim 1, furthercomprising: a memory storing a plurality of temperature values includingone temperature value for each of a plurality of gain values; andwherein said controller is configured to use said gain differentialvalue to retrieve a corresponding temperature value from said memory.11. A thermal sensor system, comprising: a central control block,comprising: a control and measurement network which provides a gainvalue, a voltage select value, and a site select value, and whichreceives a selected comparison metric; a voltage control network whichreceives said voltage select value and which provides a correspondingcentral control voltage; and a gain block which receives said gain valueand which provides a central gain voltage indicative thereof; aplurality of local measurement blocks, each comprising: a thermalsensor; a current device which applies a selected control voltage tosaid thermal sensor which develops a sensor current; a current mirrornetwork which amplifies said sensor current based on a selected gainvoltage and which provides a corresponding drive current; and a currentcompare sensor which receives said drive current and which provides alocal comparison metric indicative thereof; and select logic whichreceives said site select signal, and which selectively interfaces saidcentral control voltage, said central gain voltage, and said selectedcomparison metric to said selected control voltage, said selected gainvoltage, and said local comparison metric, respectively, between saidcentral control block and a selected one of said plurality of localmeasurement blocks.
 12. The thermal sensor system of claim 11, whereinsaid control and measurement network is configured to provide areference gain value and a reference voltage select value and to receivea corresponding reference comparison metric, and then to provide a deltavoltage value and to adjust said gain value relative to said referencegain value until said selected comparison metric is substantially equalto said reference comparison metric to determine a gain differentialvalue indicative of a temperature level.
 13. The thermal sensor systemof claim 12, further comprising: a memory storing a plurality oftemperature values including one temperature value for each of aplurality of gain values; and wherein said control network is configuredto use said gain differential value to retrieve a correspondingtemperature value from said memory.
 14. A method of measuringtemperature, comprising: applying a reference voltage level and a deltavoltage level to at least one thermal sensor which develops a referencecurrent signal and a delta current signal; comparing the referencecurrent signal and the delta current signal and providing a comparisonmetric; adjusting a gain of the delta current signal until itsubstantially matches the reference current signal as indicated by thecomparison metric and determining a gain differential between the deltaand reference current signals; and determining a temperature value basedon the gain differential.
 15. The method of claim 14, wherein saidapplying a reference voltage level and a delta voltage level comprises:applying the reference voltage level to a first thermal sensor; andapplying the delta voltage level to a second thermal sensor.
 16. Themethod of claim 14, wherein said applying a reference voltage level anda delta voltage level comprises applying the reference voltage level toa first thermal sensor and then applying the delta voltage level to thefirst thermal sensor.
 17. The method of claim 14, wherein said comparingthe reference current signal and the delta current signal comprisesapplying the reference voltage level and the delta voltage level to atleast one voltage controlled oscillator which develops an oscillatingsignal indicative thereof.
 18. The method of claim 14, wherein saidadjusting gain comprises programming a gain of a current mirror whichmirrors said delta current signal.
 19. The method of claim 14, whereinsaid determining a temperature value comprises retrieving thetemperature value from a memory using the gain differential.
 20. Themethod of claim 14, further comprising applying an offset compensationto the reference current signal.